This is a Mimio document I put up in my room when the students are working independently. I use it during writing and Daily 5 groups. This way the student don't need to raise their hand or come talk to me because of bathroom issues.
They just drag their name to a pink or blue square. You will need to go in a type their names. At first there might be a rush of kids wanting to "use the restroom," but it gets old and they don't abuse it anymore.
Pictures are from My Cute Graphics.